From Ron Miller at The Maryland Injury Lawyer Blog: "When to Get Your Experts Lined Up"--
[A]ssuming you have a very serious injury car or truck accident case and you need an expert, get the experts on board early. How do you know you need one? Do you have a problem with speed, with drinking, with highway design, with a “dangerous condition?” Well, you won’t know if you have any of those things if you don’t investigate your claims properly.
There's lots more advice in the full post--be sure to check it out.